Molybdenum metabolism will be studied in Klebsiella pneumoniae and Azotobacter vinelandii. The biosynthetic pathway of molybdenum into the iron molybdenum cofactor (FeMo-co) of nitrogenase will be investigated. Mutants are available in a number of steps in the pathway, and these will be used to establish steps in the pathway. Intermediates will be purified and characterized with respect to their composition and other properties whenever possible. A long-term goal of the project will be to completely define the pathway of FeMo-co biosynthesis from uptake of molybdate and other molybdenum compounds to the insertion of the cofactor into the FeMo-co--less dinitrogenase. The nifQBNE and V gene products are involved in FeMo-co biosynthesis. These proteins and any other proteins found to be involved in FeMo-co biosynthesis will be purified and characterized. Protein is a limiting factor in human nutrition, and biological nitrogen fixation is the largest source of fixed nitrogen for protein synthesis on earth. Molybdoenzymes are important in human nutrition and in every biological system. The study of molybdenum metabolism and nitrogen fixation will provide information about how biological systems assimilate and process this important trace element.